Omar starts counting at 21, and he counts by fours. If 21 is the 1st number that Omar counts. what is the 12th number that he counts?
Solution: What is the first number that he counts? $21$ What is the second number that he counts? $\begin{align*}&21 + 4 \\ &= 25\end{align*}$ What is the third number that he counts? $\begin{align*}&21 + 4 + 4 \\ &= 21 + (2 \times 4) \\ &= 29\end{align*}$ What is the 12th number that he counts? $\begin{align*}&21 + (11\times4) \\ &= 21 + 44 \\ &= 65\end{align*}$